This invention relates to the detection of RF leakage from communication circuits. It is disclosed in the context of an RF leakage detection system for a CATV system, but is believed to be useful in other applications as well.
Techniques for the detection of RF leakage from CATV systems are known. There are, for example, the systems described in U.S. Pat. Nos. 5,608,428; 5,294,937; 4,520,508; 4,491,968; 4,413,229; 4,237,486; 4,072,899; 3,711,767. There are also the systems described in U.S. Pat. Nos. 5,585,842; 5,493,210; 5,321,089; 5,210,498; 5,210,497; 4,962,358; 4,814,694; 4,810,961; 4,775,839; 4,731,586; 4,670,789; 4,609,866; 3,882,287; 3,684,823; 3,368,031; 3,345,560; 3,155,897; and, 2,291,533. There is also the disclosure of U.S. Ser. No. 08/690,122, filed Jul. 31, 1996. There is also the disclosure of Archer S. Taylor, Characterization of Cable TV Networks as the Transmission Media for Data, IEEE Journal on Selected Areas in Communications, vol. SAC-3, no. 2, March 1985, pp. 255-265. The disclosures of all of these references are hereby incorporated herein by reference. This listing is not intended as a representation that the disclosures listed above are pertinent, or that a thorough search of the prior art has been conducted, or that no more pertinent disclosures than those listed above exist, and no such representations should be inferred.
According to a first aspect of the invention, a communication circuit carries at least one signal including synchronizing intervals by which output of the signal by first apparatus coupled to the communication circuit is to be synchronized. A communication method includes selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals.
Illustratively according to this aspect of the invention, the method further includes transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected for determining whether the signal is escaping from the circuit.
Further illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of at least a portion of the duration of at least some of the synchronizing intervals.
Additionally illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating at least a portion of the duration of at least some of the synchronizing intervals.
Illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes generating a first sinusoid having a first frequency, generating a second sinusoid having a second frequency, frequency modulating the first sinusoid with the second sinusoid to produce a frequency modulated signal, and modulating at least a portion of the duration of at least some of the synchronizing intervals with the frequency modulated signal.
Further illustratively according to this aspect of the invention, detecting the modulation includes detecting the frequency modulated signal.
Alternatively illustratively according to this aspect of the invention, detecting the modulation includes detecting the second sinusoid.
Alternatively illustratively according to this aspect of the invention, detecting the modulation includes detecting the first sinusoid.
Additionally illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of at least a portion of the duration of a relatively constant portion of the synchronizing intervals.
Illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating at least a portion of the duration of substantially all of the synchronizing intervals.
Further illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of substantially all of the duration of at least a portion of the synchronizing intervals.
Additionally illustratively according to this aspect of the invention, selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating substantially all of the duration of at least a portion of the synchronizing intervals.
According to another aspect of the invention, a communication circuit carries at least one signal including synchronizing intervals by which output of the signal by first apparatus coupled to the communication circuit is to be synchronized. A modulator is provided for selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals.
Illustratively according to this aspect of the invention, the apparatus further includes a detector for transportation along the circuit. The detector is adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected for determining whether the signal is escaping from the circuit.
Further illustratively according to this aspect of the invention, the modulator includes a modulator for selecting and modulating the amplitude of at least a portion of the duration of at least some of the synchronizing intervals.
Additionally illustratively according to this aspect of the invention, the modulator includes a modulator for sinusoidally modulating at least a portion of the duration of at least some of the synchronizing intervals.
Illustratively according to this aspect of the invention, the modulator includes a modulator for generating a first sinusoid having a first frequency, generating a second sinusoid having a second frequency, frequency modulating the first sinusoid with the second sinusoid to produce a frequency modulated signal, and modulating at least a portion of the duration of at least some of the synchronizing intervals with the frequency modulated signal.
Further illustratively according to this aspect of the invention, the detector includes a detector for detecting the frequency modulated signal.
Alternatively illustratively according to this aspect of the invention, the detector includes a detector for detecting the second sinusoid.
Alternatively illustratively according to this aspect of the invention, the detector includes a detector for detecting the first sinusoid.
Additionally illustratively according to this aspect of the invention, the modulator includes a modulator for modulating the amplitude of at least a portion of the duration of a relatively constant portion of the synchronizing intervals.
Illustratively according to this aspect of the invention, the modulator includes a modulator for sinusoidally modulating at least a portion of the duration of substantially all of the synchronizing intervals.
Further illustratively according to this aspect of the invention, the modulator includes a modulator for modulating the amplitude of substantially all of the duration of at least a portion of the synchronizing intervals.
Additionally illustratively according to this aspect of the invention, the modulator includes a modulator for sinusoidally modulating substantially all of the duration of at least a portion of the synchronizing intervals.
According to yet another aspect of the invention, a communication circuit carries at least a first signal including frequencies in at least a first frequency band. A method of determining whether the first signal is escaping from the circuit includes transporting along the circuit apparatus adapted for receiving the first signal, detecting whether a received signal includes frequencies in the first frequency band, and producing an indication that the received signal includes frequencies in the first frequency band.
Illustratively according to this aspect of the invention, transporting apparatus adapted for receiving the first signal includes transporting apparatus through an environment including at least a second signal including frequencies in at least a second frequency band not including frequencies in the first frequency band.
Further illustratively according to this aspect of the invention, the method includes detecting whether a received signal includes frequencies in the second frequency band.
Additionally illustratively according to this aspect of the invention, the method includes comparing the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band. Producing an indication that the received signal includes frequencies in the first frequency band includes producing an indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band.
Illustratively according to this aspect of the invention, comparing the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band and producing an indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band together include comparing the magnitude of received frequencies in the first frequency band to a first desired threshold and producing a third signal based upon this comparison, comparing the magnitude of received frequencies in the second frequency band to a second desired threshold and producing a fourth signal based upon this comparison, and combining the third and fourth signals to produce the indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band.
According to yet another aspect of the invention, a detector is provided for transporting along the circuit for determining whether the first signal is escaping from the circuit. The detector is adapted for receiving the first signal, detecting whether a received signal includes frequencies in the first frequency band, and producing an indication that the received signal includes frequencies in the first frequency band.
Illustratively according to this aspect of the invention, the detector is adapted for receiving a second signal including frequencies in at least a second frequency band not including frequencies in the first frequency band.
Illustratively according to this aspect of the invention, the detector is further adapted for comparing the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band, and producing an indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency.
Illustratively according to this aspect of the invention, the detector compares the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band and produces an indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band by comparing the magnitude of received frequencies in the first frequency band to a first desired threshold and producing a third signal based upon this comparison, comparing the magnitude of received frequencies in the second frequency band to a second desired threshold and producing a fourth signal based upon this comparison, and combining the third and fourth signals to produce the indication of the relationship of the magnitude of received frequencies in the first frequency band to the magnitude of received frequencies in the second frequency band.